There has been proposed an inkjet printer including a detachable main tank, a sub-tank configured to store therein ink supplied from the installed main tank, and an image recording unit configured to record an image by discharging the ink stored in the sub-tank. Internal spaces of the main tank and the sub-tank open to the atmosphere. For this reason, when the main tank is installed in the inkjet printer, the ink moves so that liquid levels of the main tank and the sub-tank are to be the same height, by a difference (hereinafter, referred to as “water head difference”) between a water head of the internal space of the main tank and a water head of the internal space of the sub-tank. Then, when the water head difference is substantially solved (hereinafter, referred to as “equivalent state”), the movement of ink is completed.